The present invention generally relates to a semiconductor memory device and an operation method thereof, and more particularly, to a semiconductor memory device capable of improving threshold voltage distribution, and a method of operating the same.
A semiconductor memory device may be generally divided into a volatile memory device and a non-volatile memory device.
The volatile memory device has a high write and read rate, but when power supply is interrupted, stored data may be lost. The non-volatile memory device has a relatively lower write and read rate than the volatile memory device, but even though power supply is interrupted, stored data is maintained. Accordingly, the non-volatile memory device for storing data, which needs to be maintained regardless of whether power is supplied, is used. The non-volatile memory device includes a Read-Only Memory (ROM), a Mask ROM (MROM), a Programmable ROM (PROM), an Erasable Programmable ROM (EPROM), an Electrically Erasable Programmable ROM (EEPROM), a flash memory, a Phase-change Random Access Memory (PCRAM), a Magnetic RAM (MRAM), a Resistive RAM (ReRAM), a Ferroelectric RAM (FRAM), and the like. The flash memory among of the non-volatile memory device may be divided into a NOR type and a NAND type.
Especially, the flash memory has an advantage of the RAM in which program and erase of data are free, and an advantages of the ROM in which even though power supply is interrupted, stored data may be preserved. The flash memory is widely used as a storing media of a portable electronic device, such as a digital camera, a personal digital assistant (PDA), and an MP3 player.
However, a range of threshold voltage distribution of memory cells of the flash memory is increased due to various factors. It is necessary to improve reliability of the semiconductor memory device by improving threshold voltage distribution of the memory cells of the flash memory.